statistics

• Significance - the difference/association between two sets of data is greater than what would occur by chance. To find out if the difference/association is significant we need to use a statistical test
• Probability

  Probability is about likelihood. The accepted level of probability in psychology is 0.05. This is at which a researcher decides to accept or reject the null hypothesis. Even though psychologists may find statistically significant differences/relationships within data, they can never find statistical certainties.
• Calculated and critical values

  The researcher uses a statistical test to produce a calculated value. The calculated value is compared with a critical value to decide whether the result is significant or not. The critical value for a particular test are given in a table of critical values.
• Finding the critical value

  To find the critical value, we need to know :

  1. the significance level (usually 0.05)
  2. The number of participants in the investigation (N value) or the degrees of freedom
  3. whether the hypothesis is directional or non directional.
• Sign test

  Used to analyse the difference in scores between related items e.g. repeated measures and nominal data

  Calculate :

  1. The score for condition B is subtracted from condition A to produce the sign of difference (plus or minus)
  2. Add up the pluses and minuses
  3. Participants who have the same in condition A and B have to be deducted/ignored
  4. The S value is the total of the less frequent sign.

  If S is equal or less than the critical value then S is significant and the directional hypothesis is accepted and null rejected
• A=independent groups

  B=repeated measures

  C=association/correlation

  D=nominal data

  E=ordinal data

  F=interval data

  G=chi squared

  H=sign test

  I=chi squared

  J=mann whitney u

  K=wilcoxon

  L=spearmans rho

  M=unrelated t test

  N=related t test

  O=pearson's r

  
• Levels of measurement

  Nominal data - categories

  ordinal data - placed in order, intervals are subjective

  Interval data - units of equal, precisely defined size.